Substrates having a microlens array on one side thereof and an array of self-aligned apertures on the other side thereof, are widely used as optical components in computer displays (monitors), projection televisions, flat panel displays and televisions, and many other optical applications. As is well known to those having skill in the art, a microlens array includes a large number of microlenses, at least one dimension of a base of which (a “base dimension”) is less than about 500 μm in size. Hemispherical, anamorphic, lenticular and/or other conventional microlens arrays may be formed. The self-aligned apertures may be created in a layer, such as an opaque and/or reflective layer, by impinging a laser through the microlenses onto the layer.
For example, U.S. Pat. No. 4,172,219 to Deml et al., entitled Daylight Projection Screen and Method and Apparatus for Making the Same, issued Oct. 23, 1979, describes such a technique for forming self-aligned apertures. As noted in the Abstract of Deml et al., a layer of material which absorbs incident focused laser light and undergoes a resultant heating is arranged in the focal plane of a lens matrix. Laser light is projected onto such layer through the lens matrix itself. The laser light is focused by the lens elements of the lens matrix onto the layer effecting a highly localized heating of small well-defined portions of the layer. At those small well-defined portions, the material of the layer, as a result of the highly localized heating, removes itself to form the apertures of a lens-aperture matrix which is thereafter used in cooperation with the lens matrix as a rear projection or daylight projection screen.
Another technique for creating self-aligned apertures in a layer is described in U.S. Pat. No. 4,666,248 to van de Ven, entitled Rear-Projection Screen, issued May 19, 1987. As noted at Column 3, lines 51-61 of the van de Ven patent, a method of manufacturing a rear-projection screen in accordance with the invention is characterized in that the following steps are carried out in the given sequence: replicating on a first side of a thin transparent foil an anamorphotic lens structure formed in a mould, applying a light-sensitive material to the second side of the transparent foil, exposing the light-sensitive material through the lens structure, developing the light-sensitive material in such a way that non-exposed parts become opaque, and attaching the second side of the foil to a transparent supporting sheet.
Yet other techniques for forming self-aligned apertures are described in U.S. Pat. No. 6,967,779 to Fadel et al., entitled Micro-Lens Array With Precisely Aligned Aperture Mask And Methods Of Producing Same, issued Nov. 22, 2005, and assigned to the assignee of the present application. As noted in the Abstract of the Fadel et al. patent, a micro-lens array with a precisely aligned aperture mask, and a method of forming the same, is provided. The aperture mask is formed by projecting light onto a mask layer using each lenslet in the micro-lens array. The intensity of the light and the mask layer material are chosen so that the light forms apertures in the mask layer via a non-ablative process. The resulting apertures are automatically aligned with their respective lenslets.
Despite the disclosure of self-aligned aperture formation techniques using a laser beam in the Deml et al. patent over 25 years ago, commercial use of laser beams to create self-aligned apertures through a microlens array do not appear to be widespread. In particular, since a laser produces a relatively small beam of light, aperture creation processes for large substrates, such as substrates having at least one dimension that is about 30″ or more, and/or for continuous processing of webs, may provide low throughput. Moreover, it may be difficult to control the laser beam as it scans the array, which may result in misalignment of the apertures relative to the microlenses. Misaligned apertures may, in turn, create variation in transmission leading to unacceptable visible defects when the substrates are used in optical applications.